1. Field of the Invention
This invention relates generally to chemical mechanical planarization or polishing (CMP) tools and, more particularly, to a device for supporting and maintaining proper alignment of a probe for measuring film thickness during a chemical-mechanical rinse phase of wafer processing.
2. Description of the Related Art
Briefly, the chemical mechanical polishing process requires that a workpiece be held, with the desired coated surface face down, on a polishing pad supported on a rotating table, in the presence of an abrasive slurry. A chemical mechanical polishing machine can include a single rotating polishing plate and a smaller diameter rotating wafer carrier to which a wafer (or wafers) is (are) mounted. The wafer carrier is held above the polishing plate, in either a stationary fixed position or oscillating back and forth in a predetermined path, while both polishing plate and wafer carrier are rotated about their respective center axes. A slurry, consisting of an abrasive suspension with or without an etching reagent, is fed onto the polishing plate during polishing of the wafer. The slurry, also referred to as a carrier liquid, can be selected to include an etchant for the coating being planarized and for not substantially attacking other materials involved in the process. The slurry is further fed between the polishing plates to polish and flush away the material removed from the semiconductor wafer. Current chemical mechanical polish CMP tools are built with a constrained processing sequence whereby wafers are loaded from a cassette, polished, rinsed, cleaned, dried and unloaded. In some cases there are multiple polish steps where a wafer is polished first in one polishing medium, rinsed, polished in a second medium, rinsed, cleaned, dried and unloaded.
Further, when a CMP process polishes transparent materials such as oxides and nitrides in addition to metals, the process is typically controlled by using these same optical film thickness measurement. For example, back end silicon dioxide layers are typically polished from a starting thickness of 20000 angstroms to a final thickness of 10000 angstroms. To control the process, wafers have to be removed periodically from the spin dryer and measured on an optical film thickness measurement tool that examines the film reflectivity spectrum across a range of optical wavelengths to determine the thickness of material from the optical fringe pattern. Thickness measurements are typically made at many points on the wafer (usually six or more). The deviation of this thickness value from a desired value is used to adjust the polish time for subsequent wafers up or down to assure that they are polished to the correct thickness.
The measurement of thin films on semiconductor and other micro-manufactured parts is typically performed by an optical interference technique in which the reflectance or transmission properties are measured using an optical probe using a separate apparatus. Then, the acquired spectrum is analyzed with a computer program using known film properties and physics to solve for unknown properties such as film thickness, density etc. For ideal films having one or more perfectly flat layers, these measurements are straight forward and well documented.
In particular, when using these various CMP polishing tools in processing a wafer where a sufficient amount of surface films has been polished (removed by grinding), the wafer is rinsed and cleaned to remove slurry and then dried in a spin-dry process in separate processing stages using a particular tool. This is time consuming and introduces error into the processing of wafers. Indeed, prior to the invention, no effective device has existed that can properly support a film thickness measurement probe in a rinse tank of a CMP polishing tool, thereby allowing this critical process control information to be acquired immediately and simultaneously after the wafer leaves the polishing section of the CMP tool to be rinsed.
In view of the foregoing and other problems, disadvantages, and drawbacks of CMP polishing tools, it is a principal object of the present invention to provide a precision alignment and support structural assembly for an optical film measurement probe in the wafer rinse tank of a CMP polish tool.
It is therefore another object of the invention to provide a support and alignment device that saves significant process time and improves CMP process control loop effectiveness.
The invention provides a support and alignment device within a rinse tank of the chemical-mechanical polishing (CMP) tool, wherein the device includes a probe carrier member that is mechanically coupled to a support ring using a retaining assembly comprised of springs and sliding couplings, said retaining assembly allowing motion of said probe carrier member and also bias said probe carrier against a carrier chuck member for holding and positioning a workpiece, bearings that maintains relative positioning of said probe carrier with said carrier chuck member; and a void within said probe carrier member configured for accepting a film measurement probe. The device can further include a water spray nozzle that is attached to said probe carrier.
Moreover, the device can be incorporated with a preferred apparatus for cleaning and providing surface measurements of the workpiece, wherein the apparatus includes a chemical mechanical polishing (CMP) rinse tank having a film measurement probe attached to a carrier probe member retained is said tank, said probe is for determining surface condition of said work piece; and a process controller for providing film thickness measurement of said workpiece. The process controller includes a spectrometer; and said at least one measurement probe comprises at least one multipass optical probe operatively coupled to said spectrometer, wherein each said multipass optical probe comprising: a light source for emitting a light; a light collector or detector for receiving said light; and a retroreflective element configured such that light propagating, in a first direction, from the probe to a work piece and passing through and reflecting from said work piece, is retro-reflected back in a second direction opposite the first direction so as to pass through and reflect from said work piece a total of at least two times.
Another embodiment of the invention includes a method of integrated rinsing of a workpiece and monitoring of workpiece film thickness measurements using a rinse tank section of a chemical mechanical polishing (CMP) apparatus having a film thickness measurement probe operatively coupled to a processor, wherein the method includes measuring a film thickness of a work piece with said probe during a rinse processing of said work piece in said tank, and determining film thickness of said work piece.